Mitch -
I've seen more broken 56" Kodiaks than any other length. I'm sure their are many reasons for these bows being broken, but overdraw likely caused some.
Back in the day, my Dad had a new 56" 1960 Kodiak for a few years and he always drew it to 31-1/2". But he never broke it from shooting it.
I'm certain every vintage bow has been treated differently over the past 50 or more years, but different bows hold up to use and abuse differently.
The most important thing is to keep an eye on the laminations and glass for separation and delamination.
For 56" & 60" Kodiak, 6 to 7 inches is a good starting point for brace height. I usually start at about 6-3/4". When someone who doesn't realize that brace height is individual to the individual bow, it's weight, draw length, the arrow and the shooter, I tell them that any of my suggestions for starting points are always plus or minus 100%.
That usually gets the point across that there is no silver bullet answer that is the same for everyone.